Add `automod.message.hold` v2 event

[Nerixyz]

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Problem/Feature

The automod.message.hold event wasn't supported before, so this PR adds support for it.

Description of Changes:

• Added a mock event for automod.message.hold V2.

Checklist

• [x] My code follows the Contribution Guide
• [x] I have self-reviewed the changes being requested
• [x] I have made comments on pieces of code that may be difficult to understand for other editors
• [x] I have updated the documentation (if applicable)